In monitored and/or controlled systems, numerous parameters are monitored and displayed in order to make adjustments to the system when necessary if the monitored parameters are not within predetermined ranges. Such systems include applications in which safety and/or performance is a primary objective. Systems including such instrumentation are implemented in power plants, airplanes, automobiles and even satellites, just to name a few. In general, when a measured parameter value goes beyond a predetermined range of acceptable values, a correction is made either automatically by the system or by an operator who is monitoring the parameter values being measured. For example, in an automobile application, the engine coolant temperature may be one of the parameters being measured. The temperature is displayed on a gauge to an operator and when the temperature exceeds a certain value, the operator needs to take action to correct the situation.
As applications have become more complex and sophisticated, more and more integrated circuits have been designed and implemented to maximize system monitoring and control. In general, operators prefer a gauge indication of the value of a measured parameter rather than merely an indicator light because it permits greater awareness of a developing situation or a trend, and also allows the operator or the system to be more responsive and in control. Accordingly, the use of and applications for gauges have increased over the years. With the implementation of integrated circuitry and microcontrollers, including microprocessors, many more parameters can be measured and displayed to an operator, much more rapidly and accurately than ever before.
In many applications, none or very little of the processing circuitry is multiplexed. Multiplexing allows reduction of the number of components in the system and minimization of the space needed for the processing control circuitry. Multiplexing allows circuit sharing such that one circuit may be used to process the same information, in time sequence, for a plurality of measured parameters. In the past, systems have been implemented which utilize selected and separate blocks or addresses in memory to store measured parameter values so that the same processing circuitry, by sequentially addressing appropriate addresses in memory, can be multiplexed and shared by all of the measured parameters in processing and displaying measured parameter values.
While such system implementations have been of significant value in reducing the component count, integrated circuit chip size and integrated circuit cost, there is a continuing demand for further improvement in those design areas. For example, in the prior art gauge display systems, even with the above described improvements, each circuit used to process and effect the display of measured parameter information still requires a separate operational amplifier to drive the gauge display. In terms of integrated circuit or chip area, each operational amplifier may require, for example, up to 20% or more of the space taken by an on-board CPU. In most systems where there are a significant number of parameters to be monitored, the semiconductor integrated circuit area requirements of the operational amplifiers greatly exceed the area saved through the above described parameter-based memory addressing scheme.
For example, typical gauges in an automotive instrument cluster consist of orthogonally wound coils with a magnetized disk which is free to rotate in the coils. A pointer attached to the disk can be made to point to a known location by controlling the magnitude of the currents in the two coils. Typically the current can be set as the voltage across the coils or a current source can supply the current into the coil. To maintain the current in the coils, dedicated circuitry is used to set the current and hold it at a value representative of a measured value. This is usually a Digital-To-Analog Converter (DAC) driving dedicated coil driver amplifiers. Hence for a full cluster of six gauges (i.e. 12 coils), six DACs and twelve amplifiers are required. Similarly, for a current source approach, six DACs and twelve Voltage-to-Current (V-I) conversions would be required.
Thus there is a need for an improved method and apparatus for processing measured parameter information and displaying such information on display devices wherein such method and apparatus may be implemented using a substantially reduced number of component parts and a significantly smaller integrated circuit surface area.